Dynamical, Strong-Field Gravity

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This award supports research in relativity and relativistic astrophysics and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. The research goals of this project are focused on understanding the strong-field regime of Einstein's theory of general relativity. This encompasses both astrophysical and theoretical aspects of general relativity. On the astrophysical side, the main effort is numerical simulation of binary black hole, black hole-neutron star and binary neutron star collisions. This is important to support the nascent field of gravitational wave astronomy that began in 2015 with LIGO's detection of the collision of two black holes. The speed at which the field is advancing is also breathtaking, with the first gravitational wave detection of a binary neutron star collision in 2017, accompanied by intense study of the aftermath across the electromagnetic spectrum by a large community of observational astronomers. Numerical models of such events are needed to aid in detection, and are crucial to decipher details of what happened. On the theoretical side, there are many outstanding questions about the nature of spacetime in extreme situations. One example is the nature of singularities predicted by Einstein's theory to occur deep in the interior of black holes. Though not thought to be observable as no information can escape from black holes, how general relativity breaks down here is still of keen theoretical interest, as it will give clues to what a putative theory of quantum gravity needs to accomplish to resolve classical singularities. The pursuit of these projects will involve graduate students, undergraduates and postdoctoral fellows. They will be trained to do leading scientific research, become knowledgeable in corresponding areas of physics, and adept in high-performance computing and numerical methods. These skills are invaluable to many professions, and would thus also benefit and further the development of those students and postdocs that subsequently wish to pursue careers outside academia.A specific list of gravitational wave source modeling projects that will be pursued are (1) understanding the consequences of neutron star spin in binary neutron star and black hole-neutron star mergers, (2) developing methods to detect mergers that occur with high orbital eccentricity, (3) using properties of the quasi-normal ringdown of the remnant black holes in binary black hole collisions to test general relativity, in particular the uniqueness properties of black holes, (4) developing models of mergers in certain modified gravity theories to better understand how observations can either rule out such modified scenarios, or detect novel physics beyond general relativity. Regarding black hole interiors, the initial problem will be to study the nature of rotating BTZ (Banados-Teitelboim-Zanelli) black holes formed during gravitational collapse in 3-dimensional asymptotically Anti de-Sitter spacetime. This offers a simplified scenario compared to forming Kerr black holes in four-dimensional spacetime, the ultimate goal of this line of research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.